Viewing 1-12 of 150For many urbanites, summer means being constantly dripped on from the air conditioners that fill virtually every city window. These ubiquitous boxes must consume a tremendous amount of energy. From an environmental perspective, aren't central air conditioners better?Air conditioning accounts for more than 15 percent of the energy use of the average home—somewhere around 183 billion kilowatt-hours of electricity in the United States per year, according to a 2001 analysis by the Energy Information Administration. Generating that much electricity creates about 119 million tons of carbon dioxide, or roughly the amount of CO2 spewed by 20 million cars each year. Remarkably, the percentage of homes with central air more than doubled, from 27 to 55 percent, between 1980 and 2001. When deciding on how to air-condition your abode, you have two basic choices: single-room units or a centralized system. Anyone who's been to a big-box hardware store has seen the single-room air conditioners.

They're heavy, steel boxes designed to wedge into a window and dangle precariously over passing pedestrians. (In case you were wondering: Yes, they do fall on people.) Inside, there's a condenser, an evaporator, a thermostat, and a couple of fans. Central air conditioners have a different structure altogether. The condenser typically sits on the roof or in the backyard. A set of pipes runs coolant from the condenser into an air handler, which is usually located near the home's furnace. The air handler blows the cooled air through the home's duct system and into individual rooms. A central air system's energy efficiency is measured two ways. The more basic rating is the energy efficiency ratio, or EER, which describes the unit's energy consumption while cooling a prescribed volume of 95-degree air over the course of an hour in a specialized laboratory. The seasonal energy efficiency ratio, or SEER, is a bit more complicated and considers the average energy use at various temperatures and humidity levels.

Window units are rated only by EER, and lose out to central A/C by this metric. An Energy Star-certified central unit must have a minimum EER of 12, while window units only need to achieve between 9.4 and 10.7, depending on size, to be certified. (It's possible to buy a window unit rated higher than this minimum, but the same goes for central units. Overall, the central units are still rated higher.) One reason window air conditioners have lower ratings is that it's impossible to fit much advanced hardware into that little box. what is a through the wall ac unitWhile modern central air conditioners can work at a range of speeds, for example, the condensers in most window units only have two: on and off. ac power supply for car(This is, incidentally, the primary reason window air conditioners don't get SEER ratings.)cheap mini ac units

This can make a significant difference in energy use. Air conditioners not only lower air temperature; they also remove moisture. Just how much moisture is removed depends on how much air passes through the air conditioner. A machine that only works at full speed (or not at all) can drop a room's temperature quickly by cooling just a small volume of air to an extremely cold state. In contrast, an air conditioner with variable speed settings can have the same effect by processing a larger volume of air, but cooling each unit volume by a smaller amount. The latter situation results in greater dehumidification because more air runs through the machine. While this seems like a technical point, it's quite significant, because it means users can set central air conditioners to a higher temperature and feel just as comfortable, because the air is less humid. But the window units have their advantages, too. Central air conditioners suffer from "duct losses." As cooled air passes through the system of ducts on its way to the rooms, it warms up and often leaks through the fittings.

These losses can decrease an air conditioner's energy efficiency by up to 30 percent. Window units that block the sun from your room, buzz, and shake violently every time the condenser switches on are basically begging for attention—very few consumers walk out the door without remembering to shut off their window units. The quiet and unobtrusive functioning of central air conditioners, on the other hand, can lead to accidental overuse. Industry observers note that people tend to set their central air conditioner to a comfortable temperature and never change it. Window units also offer room-by-room control. For singletons or couples who occupy only one bedroom at night, cooling a single room consumes a small fraction of the energy that a central air conditioner would. Central air units are getting smarter, though, and accordingly more efficient. Programmable thermostats can make up for forgetful central A/C users by shutting the unit off when no one is home. Some central air systems even divide homes into separately controlled zones, so you don't have to cool the kitchen at 3 a.m. just to keep your bedroom a sleepable temperature.

And some new central air conditioners have an air handler in each room, skipping the ducts entirely, combining precise control with improved efficiency and less noise. Because of the construction and behavioral variables, it's impossible to pronounce a winner in this particular competition. As is often the case, the choice is often going to come down to each consumer's behavior. Generally speaking, the newfangled ductless system is going to be the most efficient but priciest option upfront. If you're choosing between an old-school central air system and window units, the latter could be better if you're childless, live in a large home in a dry environment, or tend to be forgetful about adjusting your thermostat. The Lantern thanks Jennifer Amann of the American Council for an Energy-Efficient Economy. Click here to see a slide show of clever and humorous cooling systems.Ductless air conditioners are ideal for houses where building new ductwork would be cost-prohibitive.

Like regular central air conditioners, ductless air conditioners are split into two main parts, an outdoor condenser and an indoor unit that handles the air circulation. If you're in the market for a ductless air conditioner, it's essential to check the BTU, or British Thermal Unit, rating, which measures cooling capacity based on square footage. On average, a single, 400- to 500 square-foot room will need between 9,000 and 10,500 BTU, so the higher the BTUs of your air conditioner, the easier it will be to cool the desired living space. In addition, look for units that have met the tough efficiency requirements of the Environmental Protection Agency, EPA, designated as Energy Star products. Consumer Reports tested three units, each with 12,000 BTUs per hour, strong enough to cool a living space of approximately 650 square feet. They found the Mitsubishi MSA12WA, the Sanyo KS1271 and the LG LS122CE to be three great values, cooling well and making little noise. The Mitsubishi unit can be purchased online at Amazon, and both the Sanyo and LG units can be bought directly from the manufacturer's website, as well as from Home Depot and Amazon.

At $1,000, the LG LS122CE is the least expensive of the units, with the Sanyo KS1271 priced at $1,090 and the Mitsubishi MSA12WA a little higher at $1,200. This does not include parts and labor needed for a professional installation. The U.S. Department of Energy gives every air conditioning unit a “seasonal energy efficiency ratio,” or SEER. This is measured by calculating a unit's BTU output over a year, divided by its total energy input. The higher the SEER, the more energy efficient the unit, and if you buy an air conditioner with a SEER of 16 or more, you can qualify for a federal tax credit of 30 percent, up to $1,500, on parts and labor for professional installation. Setting up a ductless air conditioner unit requires cutting a hole in your exterior wall. You must know where your electrical wiring is located and must have expert measurements for installing tubing from the outside condenser into the indoor unit. Unless you hire a licensed contractor to do the job, you risk improper installation.